I figured this out by looking through the web2py source code. Apparently, web2py is set up to do what I want to do for a particular debugger, seemingly called Wing Db. There's a constant env var ref in the code named WINGDB_ACTIVE that, if set, redirects exceptions to an external debugger.
All I had do to was define this env var, WINGDB_ACTIVE, as 1 in my PyCharm execution configuration, and voila, exceptions are now passed through to my debugger!